Elastic polyesters which are used for fibers, molding materials and films have been hitherto produced by batch processes as disclosed in, for example, Japanese Patent Publication Nos. 4116/1973 and 49037/1977 by melting a mixture of crystalline polyester chips and lactones with heating and reacting them in a batch-wise operation.
However, in batch processes, there is a drawback such as polymers having stable color tone can be hardly obtained. Further, it is difficult to remove unreacted lactones in batch processes, which produces bad smell in resulting polymers. In addition, batch processes have many disadvantages from economical viewpoint.
Under these circumstances, the present inventors have intensively studied to eliminate the above drawbacks of conventional batch processes and to find out most advantageous process and operating conditions. As the result, it has been found that it is possible to carry out the production of elastic polyesters by a continuous process without the above drawbacks. Further, it has been found that it is possible to reduce a content of terminal carboxyl group in a resulting polymer by the continuous process, which improves color tone of the resulting polymer.